Transforming growth factor beta 1 is a polypeptide originally isolated from platelets which is a regulator of cell growth and differentiation. In vitro, given certain cultured conditions TGbeta 1 can cause fibroblasts to grow in soft Agar - a property of transformed cells. More often, though, TGF beta is an inhibitor of growth, for example it inhibits FGF stimulation of endothelial cell proliferation. However, it cooperates with FGF in induction of the embryonic mesoderm. TGF beta 1 also regulates production of extracellular matrix, and in particular regulates plasminogen activators and the PA inhibitor, PAI-1. Plasmin can activate latent TGF beta 1. All these features suggest that TGF beta 1 could play one or more important roles if present in the heart. In this study, we used a polyclonal antiserum raised by Flanders and Sporn against the first 30 residues of TGF beta 1. Specificity of the immunocyhtochemistry was indicated by the absence of staining with normal (non-immune) serum or with immune serum pre- absorbed with excise TGF beta 1. Immunohistochemical evidence of TGF beta1 was found in cardiac myocytes and in smooth muscle cells and endothelial cells of sections of normal rat hearts. Supportive evidence was the presence of a 2.4 Kb mRNA transcript on northern blotting. Coronary ligations were then performed in these rats. Between 1 and 6 hours after ligation ir TGF beta-1 began to be lost from cardiac myocytes, sparing only 1-2 layers of cells in the subendocardium and around vessels, which are presumably viable cells. Interestingly, by 6 hours these cells seemed to actually have an increase in immunoreactivity, as did myocytes in the border zone. These effects suggest that TGF beta-1 may will be involved in fibrinolysis, wound healing or angiogenesis in the setting of myocardial infarction.